An ear segregating for a blistered-appearing kernel phenotype was given to C.R. Burnham by the Northrup King Company about 1960. Dr. Burnham discovered that the mutant when self-pollinated could produce ears also segregating for brittle-1. This material was provided to R.L. Phillips in about 1963 for further tests. After considerable effort, the hypothesis was developed that the blistered phenotype was a result of the kernel being mosaic for bt1. Tester stocks kindly provided by B. McClintock and P.A. Peterson allowed the discovery that a two-element transposable element system comparable to Spm and En was operating, with a non-autonomous element being present at the bt1 locus. We have referred to this system as Spm-P because its independent origin may mean that it is unique, although the genetic tests have not revealed any differences via tests with McClintock's or Peterson's stocks.
Recently we have performed mapping tests in an attempt to locate Spm-P We crossed the Spm-P stock (which is a2 a2) with members of the waxy translocation series and testcrossed to a2-m-1 wx.
We analyzed 111 crosses involving the waxy translocation series. Independence of a single Spm-P element with a2 and wx was evident in all crosses involving T1-9c, 1-9(8389), 1-9(4995), 2-9d, 4-9(5657), 6-9b, and 7-9(4363). Linkage of Spm-P and a2 was indicated in 43 crosses; these data are presented in Table 1. We are discounting those cases where the apparent linkage value is around 25 map units, because this could simply reflect the independent segregation of two Spm-P elements. This result was obtained in crosses involving T2-9b (5 cases), T4-9b (1 case), T5-9a (1 case), T6-9a (2 cases), T7-9a (4 cases), T8-9d (1 case), T8-9(6673) (2 cases), and T9-10b (2 cases). A linkage value of less than 10 map units between Spm-P and a2 was found with crosses involving T3-9c (1 case), T4-9b (3 cases), T4-9g (3 cases), T5-9a (2 cases), T5-9c (4 cases), T7-9g (2 cases), T8-9(6673) (4 cases), T9-10b (3 cases). Linkage values of 10-15 map units were obtained with crosses involving T2-9b (2 cases--but1 case fits the 2 Spm-P model), T3-9c (1 case), T4-9g (1 case), and T5-9a (1 case). Linkage values of 30-40 map units were obtained in two cases with T5-9a. Crosses involving culture 25987 (T5-9c) indicated linkage of Spm-P and wx, but this probably is because a2 and wx are linked due to the T5-9c translocation.
These results indicate that Spm-P is often linked to a2 on chromosome 5. The frequency of independence is similar to that reported by Nowick and Peterson (1981, Mol. Gen. Genet. 183:440-448) for the movement of En from its initial site.
R.L. Phillips, L.G. Block, V.M. Peschke and C.R.
Burnham
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